A:①②
B:①④
C:②③
D:②④
下列各句中,划线的词语使用正确的一句是( )
已知在△ABC中,AB→=(2,3),AC→=(1,k),且∠A为直角,则k=____ .
— I saw Mr. Green at school this morning.
— No, it _____ him. He flew to Canada last week.
小球悬挂在细绳下来回摆动,请画出小球在如图位置时所受绳子拉力F和重力G的示意图.